1. Field of the Invention:
The present invention is directed to an electromagnetic driving circuit for driving a pendulum or the like.
2. Description of the Prior Art:
Turning first to FIG. 9, there is illustrated a driving circuit for detecting and driving a pendulum of, e.g., a clock by use of a coil. The operation of this circuit will now be described. When a permanent magnet M, as illustrated in FIG. 10A, approaches a coil L.sub.2, an induction voltage is generated in the coil L.sub.2 in such a direction as to repulse the magnet M. As depicted in FIG. 10B, when the magnet M is disposed opposite to the coil L.sub.2, the induction voltage comes to 0. As shown in FIG. 10C, where the magnet M moves away from the coil L.sub.2, the induction voltage is created in the coil L.sub.2 in such a direction as to attract the magnet. Polarity of the induction voltage, as illustrated in FIG. 11A or 11C, differs depending on the direction in which the coil L.sub.2 is wound.
First, the operation in the case of generating the induction voltage shown in FIG. 11A will be discussed. A base voltage of a transistor T.sub.2 is, as depicted in FIG. 11B, clamped by a given voltage V by virtue of diode properties of its base/emitter. If the base voltage of the transistor T.sub.2 decreases below a threshold voltage v.sub.t due to the induction voltage shown in FIG. 11A which is generated at a terminal p of FIG. 9, however, the transistor T.sub.2 is turned OFF. For this reason, the transistor T.sub.1 is inversely turned ON. Then a driving current flows through the coil L.sub.2 for a time t.sub.6 determined by time constants of a capacitor C.sub.1 and a resistance R.sub.1, whereby the magnet M is attractively driven.
Where the induction voltage is, as shown in FIG. 11C, generated, the base voltage of the transistor T.sub.2 is held substantially at the voltage V because of the diode properties thereof even if the voltage of the terminal p exhibits such an increase as illustrated in FIG. 11C. When the induction voltage exceeds a peak, the base voltage of the transistor T.sub.2 is lowered with a drop in the foregoing voltage. The base voltage then decreases below the threshold voltage v.sub.t, at which time the transistor T.sub.2 is turned OFF. Subsequently, the driving current, as in the former case, flows through the coil L.sub.2, thereby repulsively driving the magnet M.
For more efficient drive of the magnet, the coil is driven at a timing illustrated in FIG. 10A in the case of attraction-drive. Where the repulsion-drive is adopted, it is desirable to drive the coil at a timing shown in FIG. 10C.
In the above-described arrangement, however, the drive-timing in some cases deviates depending on the direction in which the coil is wound, with the result that a favourable driving condition with high efficiency can not be obtained. Namely, since the coil is driven at the timing shown in FIG. 10A, there arises no problem in a situation of FIG. 11A. If the winding direction is reversed, however, the repulsion-drive of the coil is, as shown in FIG. 11C, initiated from a point slightly before the timing shown in FIG. 10B, thus leading to considerable deterioration of efficiency. For this reason, it is required that the circuit be constructed, taking even the winding direction of coil into consideration at the time of manufacture.
Moreover, there is sensitivity with respect to noises of a power source, and driving pulses of the coil are often produced due to fluctuations in voltage of the power source.
The induction voltage in the aforementioned circuit is generated at the terminal p depicted in FIG. 9. If the induction voltage is greater than a reference voltage v.sub.r, the transistor T.sub.2 is turned OFF, while the transistor T.sub.1 is turned ON. As a result, the driving current flows through the coil L.sub.2. An ON-time t.sub.7 of the transistor T.sub.1 is determined by the time constants of the capacitor C and the resistance R.sub.1.
For the purpose of driving the magnet with high efficiency, it is desirable that the driving operation be effected at the timing shown in FIG. 10A, i.e., as illustrated in FIG. 12A, at the maximal point of the induction voltage V.sub.1 in the case of attraction-drive. The reference voltage v.sub.r and a driving-time t.sub.7 are adequately set to satisfy the above-described requirement.
In the great majority of cases, the drive-timing and the driving-time differ according to a length of a swing bar or a magnitude of swing angle when driving the pendulum.
In the above-mentioned circuit constitution, however, the driving-time is determined in terms of a single meaning by the time constants of the capacitor C and the resistance R.sub.1, and the time constants must therefore be adjusted each time in accordance with the length of the swing bar or the magnitude of swing angle.
In addition, the reference voltage v.sub.r has to be properly adjusted in order to vary the drive-timing.
For instance, where the same pendulum as that of FIG. 12A is employed and the swing angle is made smaller than that in the former case, an amplitude of the induction voltage, as shown in FIG. 12B, becomes small, and there are created moderate variations in amplitude. In this case, the drive-timing has to be so adjusted that the driving pulses are generated at the maximal point of the induction voltage by adjusting the reference voltage v.sub.r. Besides, it is necessary to cause the driving current to flow through the coil for a time t.sub.8 longer than the above-mentioned one, and the time constants of the capacitor C and the resistance R.sub.1 must be modified.
In such a case, as depicted with a dotted line of, e.g., FIG. 12A, if the driving-time is set to a value longer than the optimal time t.sub.7, it follows that the swing angle becomes larger than is required. The driving current flows at a timing when an induction voltage V.sub.2 having a reverse polarity is generated, resulting in wasteful consumption of electric current.
In a situation of FIG. 12B, as indicated by the dotted line, the driving-time is set to a value shorter than the optimal time t.sub.8 ; therefore the necessary driving forces can not be obtained, and the pendulum ceases to swing in some cases.
Where the swing bars differ in length, the same adjustment as the above-mentioned one is needed, and similar defects are created.
As discussed above, some defects inherent in the prior art circuit consitution are present: both the time constants and the reference voltage of the circuit must be adjusted each time in accordance with the magnitude of swing angle or the length of swing bar; and if some deviation is produced in the adjustment, the electric current is wastefully consumed, or the pendulum stops.
The foregoing conventional driving circuit for the pendulum can be used for a type in which the driving operation is performed by orienting two poles of the permanent magnet M, as illustrated in FIG. 13, toward the coil L.sub.2 as well as for a type in which one pole of the permanent magnet M is, as explained earlier, disposed to stand vis-a-vis with a coil L.sub.2. Description will herein be centered on the driving operation associated with the type shown in FIG. 13. As shown in FIG. 14A, the magnet M moves in a direction indicated by an arrowhead and is positioned opposite to the coil L.sub.2. At this time, the coil L.sub.2 is excited in such a direction as to stop the magnet M. Then occurs a maximal induction voltage v.sub.1 illustrated in FIG. 15A. On the other hand, when the magnet M, as depicted in FIG. 14B, moves in the reverse direction and faces to the coil L.sub.2. The coil L.sub.2 is similarly excited in such a direction as to stop the magnet M. Then a maximal induction voltage v.sub.2 shown in FIG. 15A is generated.
It is most desirable in terms of efficiency that the magnet is energized by causing the driving current to flow through the coil at the maximal point, viz., at the timing shown in FIG. 14A or 14B.
A threshold voltage of the transistor T.sub.2 depicted in FIG. 9 is set to the voltage v.sub.r shown in FIG. 15. As a result of this, if the induction voltage exceeds the voltage v.sub.r, the transistor t.sub.2 is turned OFF, while the transistor T.sub.1 is turned ON. Then, the driving current, as shown in FIG. 15A, flows through the coil L.sub.2 at the timing of the induction voltage v.sub.1 with the result that the magnet M is energized. As in the former case, some deviation is created in the timing at which the coil is driven because of fluctuations in amplitude of the induction voltage, thereby probably decreasing the driving efficiency.
Namely, as shown in FIG. 15B, when the amplitude of induction voltage diminishes, the timing at which the voltage v.sub.r is reached is delayed, and it follows that the driving current flows through the coil slower than the optimal timing.
While on the other hand, if the amplitude of induction voltage increases, the driving current flows in the coil faster than the optimal timing. In either case, there is a drop in driving efficiency. Such being the case, the deviation among the factors which exert influences on the amplitude of induction voltage must be eliminated in order to keep the driving efficiency optimal. Accuracy in manufacturing and assembling processes is strictly required.
A lengthy description of the prior art circuit constitution has been given above, but the biggest defect thereof is the incapableness of integrating the circuit constitution.